Special Issue "Ultrafast Vortex Pulses"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 June 2020).

Special Issue Editors

Prof. Dr. David Andrews
E-Mail Website
Guest Editor
School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
Interests: fundamental molecular photonics and energy transport; optomechanical forces and nonlinear optical phenomena
Special Issues and Collections in MDPI journals
Dr. Ruediger Grunwald
E-Mail Website
Guest Editor
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
Interests: nondiffracting beams; beam shaping; wavefront sensing; microoptics,; nanooptics,; structured light; orbital angular momentum; ultrashort pulse applications

Special Issue Information

Dear Colleagues,

Currently, there is a boom in studies on “twisted light”, accompanied by exciting new developments in quantum optics, fiber optics, microscopy, quantum informatics, and optical communication. With the commercial availability of ultrashort-pulsed light sources, a particular branch of this field of research has now moved into sharp focus. Ultrafast vortex pulses combine the rotational degrees of freedom of orbital angular momentum and/or spin angular momentum with the specific features of ultrashort pulses, such as temporal localization, high peak intensities, and large spectral bandwidths. The application of vortex-shaped wave-packets holds numerous kinds of promise: to provide an improved understanding of the dynamics of atomic and molecular processes, to enable the generation of unprecedented short flashes of light, to facilitate the exploitation of enhanced selectivity in interactions with material having chiral properties, to provide a means for massively parallel optical data transfer, or to furnish advanced approaches for the ultrafast excitation of magnetic materials. Our Special Edition is intended to cover the full spectrum of such activities, ranging from basic theory, over advanced methods for formation and detection, through to very recent applications of ultrafast singular optics, such as attosecond pulse generation, high-resolution imaging, and fast optical information processing. Particular emphasis will be placed on array-specific problems like self-imaging, adaptive optical methods of structured beam shaping and characterization, and the emerging capabilities of super-resolution techniques in the spatial and temporal domain.

Prof. Dr. David Andrews
Dr. Ruediger Grunwald
Guest Editors

Manuscript Submission Information

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Keywords

  • Vortex beams
  • ultrashort pulses
  • orbital angular momentum (OAM)
  • vector beams
  • spiral phase
  • chirality
  • optical helicity
  • ultrafast singular optics
  • vortex beam arrays
  • vortex detection
  • vortex plasmons
  • fiber optics
  • atmospheric propagation

Published Papers (5 papers)

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Research

Article
Ultrashort Vortex Pulses with Controlled Spectral Gouy Rotation
Appl. Sci. 2020, 10(12), 4288; https://doi.org/10.3390/app10124288 - 22 Jun 2020
Cited by 1 | Viewed by 665
Abstract
Recently, the spatio-spectral propagation dynamic of ultrashort-pulsed vortex beams was demonstrated by 2D mapping of spectral moments. The rotation of characteristic anomalies, so-called “spectral eyes”, was explained by wavelength-dependent Gouy phase shift. Controlling of this spectral rotation is essential for specific applications, e.g., [...] Read more.
Recently, the spatio-spectral propagation dynamic of ultrashort-pulsed vortex beams was demonstrated by 2D mapping of spectral moments. The rotation of characteristic anomalies, so-called “spectral eyes”, was explained by wavelength-dependent Gouy phase shift. Controlling of this spectral rotation is essential for specific applications, e.g., communication and processing. Here, we report on advanced concepts for spectral rotational control and related first-proof-of-principle experiments. The speed of rotation of spectral eyes during propagation is shown to be essentially determined by angular and spectral parameters. The performance of fixed diffractive optical elements (DOE) and programmable liquid-crystal-on silicon spatial light modulators (LCoS-SLMs) that act as spiral phase gratings (SPG) or spiral phase plates (SPP) is compared. The approach is extended to radially chirped SPGs inducing axially variable angular velocity. The generation of time-dependent orbital angular momentum (self-torque) by superimposing multiple vortex pulses is proposed. Full article
(This article belongs to the Special Issue Ultrafast Vortex Pulses)
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Article
Analysis of Hybrid Vector Beams Generated with a Detuned Q-Plate
Appl. Sci. 2020, 10(10), 3427; https://doi.org/10.3390/app10103427 - 15 May 2020
Cited by 2 | Viewed by 888
Abstract
We use a tunable commercial liquid-crystal device tuned to a quarter-wave retardance to study the generation and dynamics of different types of hybrid vector beams. The standard situation where the q-plate is illuminated by a Gaussian beam is compared with other cases where [...] Read more.
We use a tunable commercial liquid-crystal device tuned to a quarter-wave retardance to study the generation and dynamics of different types of hybrid vector beams. The standard situation where the q-plate is illuminated by a Gaussian beam is compared with other cases where the input beam is a vortex or a pure vector beam. As a result, standard hybrid vector beams but also petal-like hybrid vector beams are generated. These beams are analyzed in the near field and compared with the far field distribution, where their hybrid nature is observed as a transformation of the intensity and polarization patterns. Analytical calculations and numerical results confirm the experiments. We include an approach that provides an intuitive physical explanation of the polarization patterns in terms of mode superpositions and their transformation upon propagation based on their different Gouy phase. The tunable q-plate device presents worthy advantages, since it allows a compact and efficient generation of pure and hybrid vector beams to study these effects. Full article
(This article belongs to the Special Issue Ultrafast Vortex Pulses)
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Article
A Method to Generate Vector Beams with Adjustable Amplitude in the Focal Plane
by and
Appl. Sci. 2020, 10(7), 2313; https://doi.org/10.3390/app10072313 - 28 Mar 2020
Cited by 1 | Viewed by 1592
Abstract
We design and investigate an original optical component made of a c-cut uniaxial crystal and an optical system to generate cylindrical vector beams with an adjustable polarization state. The original optical component has a specific, nearly conical shape which allows it to operate [...] Read more.
We design and investigate an original optical component made of a c-cut uniaxial crystal and an optical system to generate cylindrical vector beams with an adjustable polarization state. The original optical component has a specific, nearly conical shape which allows it to operate like a broadband wave retarder with the fast axis oriented radially with respect to the optical axis. We show via numerical simulations, using the Debye–Wolf diffraction integral, that the focal spot changes depending on the polarization state, thus enabling the control of the focal shape. Non-symmetrical shapes can be created although the optical system and incoming beam are circularly symmetric. We explained, using Jones matrix formalism, that this phenomenon is connected with the Gouy phase difference acquired by certain modes composing the beam due to propagation to the focal plane. We present our conclusions in the context of two potential applications, namely, stimulated emission depletion (STED) microscopy and laser micromachining. The optical system can potentially be used for STED microscopy for better control of the point-spread function of the microscope and to decrease the unwanted light emitted from the surroundings of the focal point. We give an analytical expression for the shape of the original component using the aspherical lens formula for the two versions of the component: one for each potential application. Full article
(This article belongs to the Special Issue Ultrafast Vortex Pulses)
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Article
Spatial Manipulation of a Supercontinuum Beam for the Study of Vortex Interference Effects
Appl. Sci. 2020, 10(6), 1966; https://doi.org/10.3390/app10061966 - 13 Mar 2020
Viewed by 877
Abstract
In this work, we generate optical vortices from the supercontinuum output of an ultrafast laser interacting with a micro-structured fiber. Using a segmented spatial light modulator, multiple vortices are designed and dynamically generated and shifted in order to observe their superposition in the [...] Read more.
In this work, we generate optical vortices from the supercontinuum output of an ultrafast laser interacting with a micro-structured fiber. Using a segmented spatial light modulator, multiple vortices are designed and dynamically generated and shifted in order to observe their superposition in the image plane. It is shown that single-color patterns of exquisite complexity can be generated across a wide frequency range. Multi-color interference patterns are experimentally generated and compared to the results of computer simulations. Multiple vortices of varying colors are also generated and independently controlled, demonstrating that no spatial interference occurs. Experimental results are compared with theoretical and numerical simulations, showing excellent agreement. Full article
(This article belongs to the Special Issue Ultrafast Vortex Pulses)
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Article
Effects of the Coupling between the Orbital Angular Momentum and the Temporal Degrees of Freedom in the Most Intense Ring of Ultrafast Vortices
Appl. Sci. 2020, 10(6), 1957; https://doi.org/10.3390/app10061957 - 12 Mar 2020
Cited by 1 | Viewed by 746
Abstract
It has recently been shown that the temporal and the orbital angular momentum (OAM) degrees of freedom in ultrafast (few-cycle) vortices are coupled. This coupling manifests itself with different effects in different parts of the vortex, as has been shown for the ring [...] Read more.
It has recently been shown that the temporal and the orbital angular momentum (OAM) degrees of freedom in ultrafast (few-cycle) vortices are coupled. This coupling manifests itself with different effects in different parts of the vortex, as has been shown for the ring surrounding the vortex where the pulse energy is maximum, and also in the immediate vicinity of the vortex center. However, in many applications, the ring of maximum energy is not of primary interest, but the one where the peak intensity of the pulse is maximum, which is particularly true in nonlinear optics applications such as experiments with ultrafast vortices that excite high harmonics and attosecond pulses that also carry OAM. In this paper, the effects of the OAM-temporal coupling on the ring of maximum pulse peak intensity, which do not always coincide with the ring of maximum pulse energy, are described. We find that there is an upper limit to the magnitude of the topological charge that an ultrafast vortex with a prescribed pulse shape in its most intense ring can carry, and vice versa, a lower limit to the pulse duration in the most intense ring for a given magnitude of the topological charge. These limits imply that, with a given laser source spectrum, the duration of the synthesized ultrafast vortex increases with the magnitude of the topological charge. Explicit analytical expressions are given for the ultrafast vortices that contain these OAM-temporal couplings effects, which may be of interest in various applications, in particular in the study of their propagation and interaction with matter. Full article
(This article belongs to the Special Issue Ultrafast Vortex Pulses)
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